Just 20 Fish Could Overtake the Great Lakes

Twenty fish – 10 mommies and 10 daddies. That's all it could take to establish a population of the invasive and ecologically destructive bigheaded or Asian carp in the Great Lakes, according to a new report out from the Canadian government. And depending on the activity of the females, even fewer than 10 males may be needed to start a population boom in the Great Lakes that would likely be impossible to stop.

The problem with these bigheaded carp is that they are voracious eaters of plankton – the broad base of aquatic food chain – and have no natural predators. They can grow to more than 4 feet and 100 pounds. One particular species has become famous in videos for its tendency to jump high out of the water when near the sound of boat motors. They've already established themselves in the Mississippi and Illinois rivers, in some places accounting for 97 percent of the fish population. If they were to enter and set up shop in the Great Lakes, the region's $7 billion commercial and sport fishing industry could be in serious trouble.

The report notes that this small population would have a greater than 50 percent chance of successfully spawning if they were to find a viable river access point to the lakes. Lake Michigan is the most likely target, and the Chicago Area Waterway System of rivers, sanitary canals and locks would be the most likely entry point. Already, the environmental DNA of carp has been detected as close as six miles from Lake Michigan. Some worry that the carp's entrance into the Great Lakes is inevitable.

But officials aren't just standing by while these 4-footers swim their way toward the world's largest source of freshwater. Various efforts have been made to stop the carp from getting into the lake system. Officials have set up a series of "electric gates" along the Chicago Area Water System that send a low-level electrical current into the water, which causes the fish to turn around. This post from NRDC's Switchboard blog argues that the U.S. government isn't doing enough to make the infrastructural fixes needed to prevent carp from winding up in the Great Lakes. If they do finagle their way in, it won't be long before they take over the ecosystem. Within 10 years, carp would likely spread from Lake Michigan to Lake Huron and Lake Erie – an impressive impact from just 10 pairs of fish, but also a little scary.

Top image: Crews search for invasive carp species near Chicago. Credit: USACEpublicaffairs/Flickr